1. Field of the Invention
The present invention relates to image reading apparatuses and, more particularly, to an image reading apparatus used as image input means in a digital copying machine or a filing system.
2. Description of the Related Art
A digital copying machine includes an image reading apparatus for reading an image of the original and a page printer for printing the read image.
Conventionally, there is a digital copying machine capable of performing multicolor printing in black and red, for example, and having a function of copying an image of the original of two colors of black and red with the colors being reproduced and a function of editing and copying an image whereby a blue part of an image of the original of two colors of black and blue is printed in red, for example.
In such a copying machine, color discrimination is performed on an image of the original for every pixel in an image reading apparatus, and color discrimination data is provided to a page printer in synchronism with monochromatic image data read from the image of the original.
Generally, discrimination of colors of an image is carried out by performing color separation on scanning light from an image of the original with spectroscopic means such as a filter, a prism, or the like and comparing the light intensity of respective separated colors.
As described in Japanese Patent Publication No. 62-26634 (1987), in a conventional image reading apparatus, a plurality of photoelectric transfer means separated from each other are arranged in predetermined positions, scanning light of respective separated colors separated into two colors is made to be incident upon the photoelectric transfer means, respectively, and color discrimination for discriminating whether the color of each pixel is a specified color or not is performed on the basis of the ratio between the levels of output signals of respective photoelectric transfer means.
Image data is generated by quantizing outputs of respective photoelectric transfer means used in color discrimination, i.e. photoelectric transfer signals corresponding to respective separated colors and then synthesizing the outputs by signal processing. Specifically, image data obtained by scanning is optically separated and then electrically resynthesized.
In the conventional image reading apparatus, there is the possibility that image data provided to the outside of the image reading apparatus is deteriorated by discrepancy between spectral characteristics and signal processing characteristics of an optical system.